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2-stroke fuel mix ratio: oil per litre, fuel choice and shelf life

Getting the oil-to-petrol ratio right is vital on a 2-stroke engine, because the oil in the fuel is its only lubricant. This page gathers the ratios, mixing method and fuel advice from L'Atelier's guides.

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Answers are written by a language model solely from this base's documents, with numbered sources. They can be wrong and aren't legal, medical or financial advice: check the sources before any important decision.

Ratio table and common volumes

50:1 means 20 mL of oil per litre of petrol: the modern standard for Stihl, Husqvarna, Echo and most current brands. 40:1 (25 mL) suits some Japanese models such as Tanaka, 32:1 (31 mL) older pre-2000s models and 25:1 (40 mL) very old engines.

At 50:1, 5 litres of petrol take 100 mL of oil. The Stihl MS 261, in all versions, uses 1:50. Always check the ratio shown on the tool or in its manual.

Mixing method and fuel choice

Use a clean graduated container, never the tool's tank. Pour the oil first, add half the petrol and shake, then the rest and shake again. Prefer synthetic 2-stroke oil; never use 4-stroke engine oil.

E10 (10% ethanol) attacks seals and diaphragms and attracts water: avoid it on small 2-strokes when possible, or use the mix within 15 days. Ethanol-free alkylate fuel keeps 2 years or more.

Frequently asked questions

How long does a 2-stroke mix keep?

Under 30 days it is fine. Between 30 and 60 days it degrades and starting can become difficult. Beyond 60 days, discard it.

What happens if I run a mix at 1:100 by mistake?

Too little oil causes overheating and piston seizure. The opposite mistake, too much oil such as 1:25 in an engine designed for 1:50, causes plug fouling and carbon buildup.

How should I store mixed fuel?

In a metal or opaque plastic container, out of sunlight. At season's end, drain the tank and run the engine until it stalls.

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